1. Field of the Invention
The present invention relates to a method for treating a metal surface and a member treated by the method, and a refrigerant compressor using the member, and more specifically, relates to a refrigerant compressor used in a freezer where an HFC refrigerant, which does not have the risk of destroying the ozone layer, is used with an improved wear resistance of the sliding surface of a rotary shaft or a vane.
2. Background Art
As a conventional refrigerant for a freezer, R-502, which is an azeotropic mixed refrigerant including dichlorodifluoromethane (R-12) or R-22, and monochloropentafluoroethane (R-115a) is used, and such a refrigerant is preferable for an ordinary freezer. Further, a refrigerating cycle where a refrigerator oil, compatible with such a refrigerant, including a mineral oil or an alkyl benzene type oil attains a high quality in terms of reliability and durability.
However, since the above-mentioned refrigerant is highly destructive with respect to the ozone layer and thus it will destroy the ozone layer if it is discharged in the atmosphere and reach the ozone layer in the sky. The destruction of the ozone layer is caused by chlorine atoms (Cl) in a refrigerant.
Therefore, refrigerants containing little amount of chlorine such as chlorodifluoromethane (HCFC-22, R-22), and refrigerants not containing chlorine such as difluoromethane (HFC-32, R-32), pentafluoroethane (HFC-125, R-125) and 1,1,1,2-tetrafluoroethane (HFC-134a, R-134a) are considered as substitute refrigerants (hereinafter referred to as HFC type refrigerant).
Examples of refrigerator oils used for the HFC type refrigerants include those which are incompatible with the HFC type refrigerants such as a mineral oil and an alkyl benzene type oil, those which are compatible with the HFC type refrigerants such as an ester type refrigerator oil and an ether type refrigerator oil, and a mixture oil thereof.
Conventionally, the surface of a rotary shaft of a compressor such as a rotary type compressor and a reciprocating type compressor has been applied with surface treatment in order to improve the wear resistance of the sliding surface, such as the salt bath soft nitriding treatment, the ion nitriding treatment, the salt bath sulphonitriding treatment, and the electrolytic sulphonitriding treatment. However, with the refrigerant replaced by the HFC type refrigerant, and the refrigerator oil replaced by the ester type refrigerator oil or the ether type refrigerator oil, compound layers applied with the conventional treatment (mainly comprising a nitride (.epsilon.-Fe.sub.3 N)) are not sufficient in terms of wear resistance due to a high friction coefficient, and thus it is impossible to operate stably in over a long time. Therefore, an improved treatment method of a rotary shaft, a compressor comprising the treated rotary shaft, such as a rotary type compressor and a reciprocating type compressor are strongly called for.
Further, with the refrigerant replaced by the HFC type refrigerant and the refrigerator oil replaced by the ester type refrigerator oil or the ether type refrigerator oil, the material of the rotary shaft needs to be a highly elastic ductile cast iron (FCD). However, by the use of a highly elastic material, particularly the FCD, since the center hole of the rotary shaft, that is, the hole for circulating the refrigerator oil from the oil pool at the lower part of the refrigerant compressor to the upper part of the refrigerant compressor has been formed conventionally by machining, the machine work becomes difficult. Therefore, a refrigerant compressor comprising a highly elastic rotary shaft where the center hole can be formed economically and easily is strongly called for.
On the other hand, a vane for a rotary type compressor is made from SKH 51 with the surface treatment for improving the wear resistance such as the ion nitriding treatment and the CrN coating treatment, or is made from an aluminum impregnation carbon material or a fiber reinforced aluminum material.
However, with the refrigerant replaced by the HFC type refrigerant and the refrigerator oil replaced by the ester type refrigerator oil or the ether type refrigerator oil, since the friction coefficient is high in the case of the conventional surface treatment such as the ion nitriding treatment, the ester type refrigerator oil or the ether type refrigerator oil is hydrolyzed by the moisture existing in the refrigerating circuit due to a high temperature caused by the friction so as to generate an acid. In this case, a sludge such as a metallic soap is formed due to the generated acid, and thus problems occur such as accumulation of the sludge on the sliding portion of the surface of a vane, corrosion and wearing. Further, in the case of the CrN coating treatment, it involves problems such as peel-off of the coating during the operation and difficulty of production by irregularity of the coated film thickness. In the case of a vane made from an aluminum impregnation carbon material or a fiber reinforced aluminum material, since it is insufficient in terms of the mechanical strength and the wear resistance, and aggressive with respect to the counterpart roller, it is impossible to operate a rotary compressor comprising such a vane stably over a long time.
An object of the present invention is to provide a refrigerant compressor comprising a rotary shaft or a vane having a low friction coefficient of the rotary shaft or a sliding portion on the surface of the vane, and a high wear resistance even if an ester type refrigerator oil or an ether type refrigerator oil is used as the refrigerator oil, and an HFC type refrigerant is used, to provide a refrigerant compressor comprising a highly elastic rotary shaft where the center hole can be formed economically and easily, and to provide a refrigerant compressor capable of preventing the generation of a sludge on the sliding portion of the surface of a vane and operating stably over a long time. A further object of the present invention is to provide a treating method used therein.